This invention relates to new hydrophilic, crosslinked, polyurea-urethane, solid, discrete particles and to a method for their preparation. More particularly, the present invention relates to hydrophilic solid particles prepared by a process consisting of adding in droplet form
(a) a hydrophilic prepolymer comprising an isocyanate-capped polyol or mixtures thereof wherein said polyol or mixture of polyols has a reaction functionality greater than two, the total of said polyol present having an ethylene oxide content of at least 40 weight percent, before capping to PA1 (b) an agitated water reactant, the volume ratio of (b):(a) being at least 2:1 and thereafter recovering the thus formed polyurea-urethane particles therefrom. PA1 (a) a hydrophilic prepolymer comprising an isocyanate-capped polyol or mixtures thereof wherein said polyol or mixture of polyols has a reaction functionality greater than two, the total of said polyol present having an ethylene oxide content of at least 40 weight percent, before capping to PA1 (b) an agitated water reactant, the volume ratio of (b):(a) being at least 2:1 and thereafter recovering the thus formed hydrophilic, crosslinked, solid, discrete polyurea-urethane particles therefrom. The thus generated solid, discrete particles are typically characterized by having a crosslinked, i.e., non-linear, molecular network, which provides the solid particle product with a broad spectrum of improved properties.
Solid polyurethane particles are known in the prior art. See Hutzler, U.S. Pat. No. 3,655,627, and Walters, U.S. Pat. No. 3,402,149. However, the teaching of both Walters and Hutzler is of a hydrophobic prepolymer in an emulsified system by use of surfactants to obtain an emulsion. The dispersion into hydrophobic particles is thus created by emulsifiers.
Wood, U.S. Pat. No. 4,137,200, teaches a method of forming a hydrophilic polyurethane foam. There is no teaching in Wood for forming solid hydrophilic polyurethane particles.
Numerous attempts have been made in the prior art to produce hydrophilic polyurethane particles. Typical methods of forming polymeric particles have been described in the literature. Solution, suspension and emulsion polymerization have been used to form particles of the desired size. Techniques for such preparations are described in The Encyclopedia of Polymer Science and Technology, 1972, John Wiley & Sons, Inc., under the topics Suspension Polymerization at pg. 552 of Vol. 13 and Ion Exchange Polymers--Synthesis and Characteristics at pg. 700 of Vol. 7. Polymeric powders have also been formed by mechanical working or solution methods as described in the same text under Powder Coatings at pg. 544, Vol. 1, of the 1976 Supplement. The particles can be formed by pelletizing, granulating, spray-drying or chemical precipitation.
The formation of polymer particles in situ by the reaction of isocyanate-capped prepolymer being added in droplet form to an aqueous medium without the use of emulsifiers has not apparently been used before to prepare particles that are suitable for molding, coating, adhesive and other applications.